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EP0413385A1 - Process for manufacturing a sodium hydroxide caustic solution - Google Patents

Process for manufacturing a sodium hydroxide caustic solution Download PDF

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Publication number
EP0413385A1
EP0413385A1 EP90202143A EP90202143A EP0413385A1 EP 0413385 A1 EP0413385 A1 EP 0413385A1 EP 90202143 A EP90202143 A EP 90202143A EP 90202143 A EP90202143 A EP 90202143A EP 0413385 A1 EP0413385 A1 EP 0413385A1
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EP
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Prior art keywords
sodium
sodium hydroxide
solution
amalgam
aqueous solution
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EP90202143A
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German (de)
French (fr)
Inventor
Jean Verlaeten
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Solvay SA
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Solvay SA
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D1/00—Oxides or hydroxides of sodium, potassium or alkali metals in general
    • C01D1/04—Hydroxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D1/00—Oxides or hydroxides of sodium, potassium or alkali metals in general
    • C01D1/04—Hydroxides
    • C01D1/20—Preparation by reacting oxides or hydroxides with alkali metal salts
    • C01D1/22—Preparation by reacting oxides or hydroxides with alkali metal salts with carbonates or bicarbonates
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
    • C25B1/36—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in mercury cathode cells
    • C25B1/42—Decomposition of amalgams

Definitions

  • the invention relates to a process for the manufacture of aqueous sodium hydroxide detergents.
  • a method for making aqueous sodium hydroxide liquors in which an aqueous solution of sodium chloride is electrolyzed in a mercury cathode electrolysis cell, a sodium amalgam is withdrawn from the cell and the amalgam of sodium with water, in contact with graphite or carbon elements, to decompose it (JS SCONCE, "Chlorine, its manufacture, properties and uses” Reinhold Publishing Corporation, 1962, pages 127 to 199).
  • JS SCONCE "Chlorine, its manufacture, properties and uses” Reinhold Publishing Corporation, 1962, pages 127 to 199.
  • the electrolysis of the aqueous sodium chloride solution generates chlorine and the subsequent decomposition of the amalgam by water generates hydrogen and produces an aqueous solution of sodium hydroxide, generally called lye aqueous sodium hydroxide.
  • a method is also known in which a method of electrolysis in a mercury cell is combined with a method of electrolysis of a sodium chloride solution in an electrolysis cell with a membrane which is selectively permeable to cations; in this known process, the decomposition of the sodium amalgam coming from the mercury cell is carried out by means of a dilute aqueous solution of sodium hydroxide produced in the membrane cell (US-A-3321388).
  • This known process certainly improves the overall yield of the two electrolysis cells, but it does not avoid the aforementioned drawback in connection with the impossibility of dissociating the production of sodium hydroxide from the concomitant production of chlorine.
  • the invention aims to provide a method which avoids this drawback of known methods, by making it possible to regulate the electrolytic production of sodium hydroxide independently of that of chlorine.
  • the invention therefore relates to a process for the manufacture of a sodium hydroxide solution, according to which a sodium amalgam is decomposed with an aqueous medium containing dissolved sodium hydroxide; according to the invention, sodium hydroxide is used which is obtained from the treatment of an aqueous solution of sodium carbonate with lime.
  • sodium hydroxide solution is intended to denote an aqueous solution of sodium hydroxide resulting from the decomposition of the sodium amalgam with water.
  • Sodium amalgam is an alloy of mercury and sodium, generally obtained by electrolyzing an aqueous solution of sodium chloride in a mercury cathode electrolysis cell.
  • the sodium content of the amalgam is not critical for the execution of the process according to the invention. In practice, however, the proper functioning of mercury cells implies limiting the sodium content in the amalgam below 7 g / kg.
  • the preferred concentrations are those between 1 and 5 g per kg of amalgam.
  • the decomposition of the amalgam is carried out by means of an aqueous medium containing sodium hydroxide obtained by treating an aqueous solution of sodium carbonate with lime.
  • the aqueous medium is generally water.
  • the production of sodium hydroxide by reaction of an aqueous solution of sodium carbonate with lime is a well-known technique (K. WINNAKER and L. KÜCHLER "Mineral technology" translated by A. ZUNDEL, Editions Eyrolles, 1962, pages 382 to 388).
  • This causticization technique of sodium carbonate leads to the production of an aqueous hydroxide solution sodium that is used to treat amalgam.
  • the sodium carbonate solution can be obtained by any suitable means.
  • a solution obtained by debicarbonation of an aqueous solution or suspension of sodium bicarbonate is generally used, such as those obtained in the process for the manufacture of soda with ammonia (TE PANG HOU, "Manufacture of soda ", Hafner Publishing Company, 1969).
  • the debicarbonation of aqueous solutions or suspensions of sodium bicarbonate is an operation well known in the art, generally consisting in heating them, for example by means of a current of steam.
  • lime is calcium oxide or calcium hydroxide. It is preferred to use an aqueous suspension of calcium hydroxide.
  • the aqueous sodium carbonate solution is treated with lime, a dilute aqueous solution of sodium hydroxide is collected from the reaction medium, said dilute solution is evaporated in conditions set to form a concentrated solution containing, per kg, more than 186 g of sodium hydroxide, said concentrated solution is cooled to crystallize hydrated sodium hydroxide in mother water, hydrated sodium hydroxide is collected , it is heated to a temperature sufficient to melt it and the sodium amalgam is treated with molten hydrated sodium hydroxide.
  • the molten hydrated sodium hydroxide constitutes the above-mentioned aqueous medium, used to decompose the sodium amalgam.
  • the dilute aqueous solution of sodium hydroxide which is collected from the reaction of sodium carbonate with lime contains for example, in general, between 5 and 25% by weight of sodium hydroxide, more generally between 8 and 15%. It is generally contaminated with solids, coming from the reagents used in the causticization reaction (sodium carbonate and lime), in particular sodium carbonate, sodium chloride and sodium sulphate.
  • the concentrated solution collected from evaporation is then cooled to crystallize hydrated sodium hydroxide in mother liquor.
  • the cooling temperature depends on the concentration of the concentrated sodium hydroxide solution collected from evaporation, and it can easily be determined by means of the phase diagram of the NaOH - H2O system (P.
  • PASCAL "New treatise on chemistry mineral", Tome II, Premier fascicule, Masson et Cie, alias, 1966, pages 254 to 258).
  • the technique described in document US-A-1733879 can be used.
  • any means capable of separating it from the mother liquor can be used, for example filtration, decantation or centrifugation.
  • This embodiment of the process according to the invention has the advantage of avoiding the presence of impurities in the above-mentioned aqueous medium, used to decompose the sodium amalgam.
  • the evaporation of the dilute solution is controlled so that the concentrated aqueous solution contains, per kg, between approximately 468 and 321 g of hydroxide. sodium, which are the contents corresponding respectively to the eutectic mixture of the compounds NaOH.3,5H2O and NaOH.2H2O, on the one hand, and to the saturated aqueous solution of hydroxide of sodium at the temperature of this eutectic, on the other hand.
  • the concentrated aqueous solution collected from evaporation has a concentration of sodium hydroxide markedly different from 388.3 g / kg, (corresponding to the compound defined NaOH.3,5H2O), so as to facilitate the passage of impurities in the mother liquor during crystallization by cooling.
  • the concentrated solution collected from evaporation has a sodium hydroxide concentration of less than 388.3 g / kg.
  • the cooling of the concentrated solution is carried out at a temperature between, on the one hand, the solidification temperature of the eutectic mixture of the compounds NaOH.3,5H2O and NaOH.2H2O (approximately 5 ° C) and, on the other hand, the melting temperature of the defined compound NaOH.3.5H2O (approximately 16 ° C).
  • the method according to the invention allows flexibility in the operation of mercury electrolysis cells, by making it possible to adapt the operation of the cells to the sodium hydroxide market, without influencing the production of chlorine.
  • the installation shown in the figure includes a causticization unit of sodium carbonate and an electrolysis unit.
  • an aqueous solution of sodium carbonate 2 and quicklime 3 are introduced into a reaction chamber 1.
  • An aqueous suspension 4 is collected from the reaction chamber 1 comprising mainly calcium carbonate in suspension in an aqueous solution of sodium hydroxide.
  • the suspension 4 is treated in a settling chamber 5, from which a precipitate of calcium carbonate 6 and a dilute aqueous hydroxide solution are collected separately.
  • the precipitate 6 generally contains a non-negligible amount of calcium hydroxide. It is sent to a second reaction chamber 8 which is also supplied with an aqueous solution of sodium carbonate 9. After treatment on a filter 10 to separate the insoluble materials 11, the aqueous solution 12 is recycled to the reaction 1.
  • the solution 7 collected from the settling chamber 5 contains for example between 8 and 15% by weight of sodium hydroxide. It is also contaminated with various dissolved impurities, in particular sodium sulfate, sodium carbonate and sodium chloride. It is sent to an evaporator 13 where it is concentrated to a sodium hydroxide content of between 321 and 388.3 g / kg. Evaporation has the result of removing water 14 and precipitating part of the impurities, mainly sodium sulfate and sodium carbonate which are removed at 15.
  • the concentrated aqueous solution 16 which is collected evaporator 13 is then treated in a refrigerant 17, where it is cooled to a temperature between 5 and 16 ° C, so as to crystallize the compound NaOH.3,5H2O in mother liquor.
  • the crystallized compound 18 and the mother liquor 30 are collected separately.
  • the crystallized compound 18 essentially consists of hydrated sodium hydroxide of formula NaOH.3.5H2O. It is sent to a storage chamber 19, where it is heated to a temperature above its melting temperature (15.9 ° C), for example at room temperature, so as to obtain an aqueous solution 20 containing approximately 388 , 3 g of sodium hydroxide per kg.
  • the mother liquor 30 is an aqueous solution of sodium hydroxide. It is recycled in the evaporator 13, after having drawn off a purge 31.
  • the electrolysis unit comprises an electrolysis cell 21 of the mercury cathode type, associated with a sodium amalgam decomposer 22. Electrolysis units of this type are well known in the art (JS SCONCE, "Chlorine , its manufacture, properties and uses "Reinhold Publishing Corporation, 1962, pages 127 to 199).
  • the electrolysis cell 21 comprises, in known manner, a horizontal mercury cathode (not shown in the figure), flowing over the bottom of the cell and anodes (not shown) arranged opposite the mercury film, at a short distance from it.
  • An aqueous solution of sodium chloride 23 is circulated in the cell, in contact with the film of mercury and the anodes.
  • the aqueous solution is decomposed by electrolysis and chlorine 24, a sodium amalgam 25 and an aqueous solution depleted in sodium chloride 29 are collected.
  • the sodium amalgam contains for example between 2.5 and 4 g of sodium per kg. It is sent to the decomposer 22 where it is circulated against the current of the aqueous sodium hydroxide solution 20 produced in the causticization unit. In the decomposer 22 the sodium amalgam 25 and the aqueous solution 20 are brought into contact with graphite elements (not shown in the drawing). The sodium amalgam is gradually decomposed by reaction with water, leading to the generation of hydrogen 26. Mercury (or a sodium-depleted amalgam) 27 is collected 27 which is recycled in the electrolysis cell 21 and an aqueous detergent of sodium hydroxide 28.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
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  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Abstract

Process for the manufacture of a sodium hydroxide lye, according to which a sodium amalgam (22) is decomposed with an aqueous medium containing dissolved sodium hydroxide (20), originating from the treatment of an aqueous sodium carbonate solution (2) with lime (3). <IMAGE>

Description

L'invention a pour objet un procédé pour la fabrication de lessives aqueuses d'hydroxyde de sodium.The invention relates to a process for the manufacture of aqueous sodium hydroxide detergents.

On connait un procédé pour fabriquer des lessives aqueuses d'hydroxyde de sodium, dans lequel on électrolyse une solution aqueuse de chlorure de sodium dans une cellule d'électrolyse à cathode de mercure, on soutire de la cellule un amalgame de sodium et on traite l'amalgame de sodium avec de l'eau, au contact d'éléments en graphite ou en carbone, pour le décomposer (J. S. SCONCE, "Chlorine, its manufacture, properties and uses" Reinhold Publishing Corporation, 1962, pages 127 à 199). Dans ce procédé connu, l'électrolyse de la solution aqueuse de chlorure de sodium génère du chlore et la décomposition subséquente de l'amalgame par l'eau génère de l'hydrogène et produit une solution aqueuse d'hydroxyde de sodium, généralement appelée lessive aqueuse d'hydroxyde de sodium. La production d'hydroxyde de sodium implique dès lors inévitablement la production conco­mitante de chlore, à raison de 886 g de chlore par kg d'hydroxyde de sodium. Cette relation rigide entre les productions respec­tives de chlore et d'hydroxyde de sodium constitue un incon­vénient majeur du procédé qui, de ce fait, ne présente pas la souplesse nécessaire pour adapter sa production aux fluctuations des marchés respectifs du chlore et de l'hydroxyde de sodium.A method is known for making aqueous sodium hydroxide liquors, in which an aqueous solution of sodium chloride is electrolyzed in a mercury cathode electrolysis cell, a sodium amalgam is withdrawn from the cell and the amalgam of sodium with water, in contact with graphite or carbon elements, to decompose it (JS SCONCE, "Chlorine, its manufacture, properties and uses" Reinhold Publishing Corporation, 1962, pages 127 to 199). In this known process, the electrolysis of the aqueous sodium chloride solution generates chlorine and the subsequent decomposition of the amalgam by water generates hydrogen and produces an aqueous solution of sodium hydroxide, generally called lye aqueous sodium hydroxide. The production of sodium hydroxide therefore inevitably involves the concomitant production of chlorine, at the rate of 886 g of chlorine per kg of sodium hydroxide. This rigid relationship between the respective productions of chlorine and sodium hydroxide constitutes a major drawback of the process which, therefore, does not have the flexibility necessary to adapt its production to fluctuations in the respective markets for chlorine and sodium hydroxide. sodium.

On connaît par ailleurs un procédé dans lequel on associe un procédé d'électrolyse en cellule à mercure avec un procédé d'électrolyse d'une solution de chlorure de sodium dans une cellule d'électrolyse à membrane perméable sélectivement aux cations; dans ce procédé connu, la décomposition de l'amalgame de sodium provenant de la cellule à mercure est réalisée au moyen d'une solution aqueuse diluée d'hydroxyde de sodium produite dans la cellule à membrane (US-A-3321388). Ce procédé connu améliore certes le rendement globale des deux cellules d'électrolyse, mais il n'évite pas l'inconvénient précité en relation avec l'impos­sibilité de dissocier la production d'hydroxyde de sodium de la production concomitante de chlore.A method is also known in which a method of electrolysis in a mercury cell is combined with a method of electrolysis of a sodium chloride solution in an electrolysis cell with a membrane which is selectively permeable to cations; in this known process, the decomposition of the sodium amalgam coming from the mercury cell is carried out by means of a dilute aqueous solution of sodium hydroxide produced in the membrane cell (US-A-3321388). This known process certainly improves the overall yield of the two electrolysis cells, but it does not avoid the aforementioned drawback in connection with the impossibility of dissociating the production of sodium hydroxide from the concomitant production of chlorine.

L'invention vise à fournir un procédé qui évite cet incon­vénient des procédés connus, en permettant de réguler la produc­tion électrolytique d'hydroxyde de sodium indépendamment de celle du chlore.The invention aims to provide a method which avoids this drawback of known methods, by making it possible to regulate the electrolytic production of sodium hydroxide independently of that of chlorine.

L'invention concerne dès lors un procédé de fabrication d'une lessive d'hydroxyde de sodium, selon lequel on décompose un amalgame de sodium avec un milieu aqueux contenant de l'hydroxyde de sodium dissous; selon l'invention, on met en oeuvre de l'hydroxyde de sodium provenant du traitement d'une solution aqueuse de carbonate de sodium avec de la chaux.The invention therefore relates to a process for the manufacture of a sodium hydroxide solution, according to which a sodium amalgam is decomposed with an aqueous medium containing dissolved sodium hydroxide; according to the invention, sodium hydroxide is used which is obtained from the treatment of an aqueous solution of sodium carbonate with lime.

Dans le procédé selon l'invention, on entend désigner par lessive d'hydroxyde de sodium, une solution aqueuse d'hydroxyde de sodium provenant de la décomposition de l'amalgame de sodium par de l'eau.In the process according to the invention, the term “sodium hydroxide solution” is intended to denote an aqueous solution of sodium hydroxide resulting from the decomposition of the sodium amalgam with water.

L'amalgame de sodium est un alliage de mercure et de sodium, généralement obtenu en électrolysant une solution aqueuse de chlorure de sodium dans une cellule d'électrolyse à cathode de mercure. En principe, la teneur en sodium de l'amalgame n'est pas critique pour l'exécution du procédé selon l'invention. En pratique toutefois, le bon fonctionnement des cellules à mercure implique de limiter la teneur en sodium dans l'amalgame au-dessous de 7 g/kg. Les concentrations préférées sont celles comprises entre 1 et 5 g par kg d'amalgame.Sodium amalgam is an alloy of mercury and sodium, generally obtained by electrolyzing an aqueous solution of sodium chloride in a mercury cathode electrolysis cell. In principle, the sodium content of the amalgam is not critical for the execution of the process according to the invention. In practice, however, the proper functioning of mercury cells implies limiting the sodium content in the amalgam below 7 g / kg. The preferred concentrations are those between 1 and 5 g per kg of amalgam.

Conformément à l'invention, la décomposition de l'amalgame est réalisée au moyen d'un milieu aqueux contenant de l'hydroxyde de sodium obtenu en traitant une solution aqueuse de carbonate de sodium avec de la chaux. Le milieu aqueux est généralement de l'eau. La production d'hydroxyde de sodium par réaction d'une solution aqueuse de carbonate de sodium avec de la chaux est une technique bien connue (K. WINNAKER et L. KÜCHLER "Technologie minérale" traduit par A. ZUNDEL, Editions Eyrolles, 1962, pages 382 à 388). Cette technique de caustification du carbonate de sodium conduit à l'obtention d'une solution aqueuse d'hydroxyde de sodium que l'on utilise pour traiter l'amalgame.According to the invention, the decomposition of the amalgam is carried out by means of an aqueous medium containing sodium hydroxide obtained by treating an aqueous solution of sodium carbonate with lime. The aqueous medium is generally water. The production of sodium hydroxide by reaction of an aqueous solution of sodium carbonate with lime is a well-known technique (K. WINNAKER and L. KÜCHLER "Mineral technology" translated by A. ZUNDEL, Editions Eyrolles, 1962, pages 382 to 388). This causticization technique of sodium carbonate leads to the production of an aqueous hydroxide solution sodium that is used to treat amalgam.

Dans le procédé selon l'invention, il est avantageux d'utiliser une solution la plus concentrée possible en carbonate de sodium; les solutions saturées sont préférées. La solution de carbonate de sodium peut être obtenue par tous moyens adéquats. On utilise généralement une solution obtenue par débicarbo­natation d'une solution ou d'une suspension aqueuse de bicar­bonate de sodium telle que celles que l'on obtient dans le procédé de fabrication de la soude à l'ammoniaque (TE PANG HOU, "Manufacture of soda", Hafner Publishing Company, 1969). La débi­carbonatation des solutions ou suspensions aqueuses de bicar­bonate de sodium est une opération bien connue en technique, consistant généralement en un chauffage de celles-ci, par exemple au moyen d'un courant de vapeur d'eau.In the process according to the invention, it is advantageous to use a solution as concentrated as possible in sodium carbonate; saturated solutions are preferred. The sodium carbonate solution can be obtained by any suitable means. A solution obtained by debicarbonation of an aqueous solution or suspension of sodium bicarbonate is generally used, such as those obtained in the process for the manufacture of soda with ammonia (TE PANG HOU, "Manufacture of soda ", Hafner Publishing Company, 1969). The debicarbonation of aqueous solutions or suspensions of sodium bicarbonate is an operation well known in the art, generally consisting in heating them, for example by means of a current of steam.

Dans le cadre de l'invention, la chaux est de l'oxyde de calcium ou de l'hydroxyde de calcium. On préfère utiliser une suspension aqueuse d'hydroxyde de calcium.In the context of the invention, lime is calcium oxide or calcium hydroxide. It is preferred to use an aqueous suspension of calcium hydroxide.

Dans une forme de réalisation particulière du procédé selon l'invention, on traite la solution aqueuse de carbonate de sodium avec la chaux, on recueille du milieu réactionnel une solution aqueuse diluée d'hydroxyde de sodium, on soumet ladite solution diluée à une évaporation dans des conditions réglées pour former une solution concentrée contenant, par kg, plus de 186 g d'hydro­xyde de sodium, on refroidit ladite solution concentrée pour cristalliser de l'hydroxyde de sodium hydraté dans une eau mère, on recueille l'hydroxyde de sodium hydraté, on le chauffe à une température suffisante pour le fondre et on traite l'amalgame de sodium avec l'hydroxyde de sodium hydraté fondu. Dans cette forme de réalisation du procédé selon l'invention, l'hydroxyde de sodium hydraté fondu constitue le milieu aqueux précité, utilisé pour décomposer l'amalgame de sodium.In a particular embodiment of the process according to the invention, the aqueous sodium carbonate solution is treated with lime, a dilute aqueous solution of sodium hydroxide is collected from the reaction medium, said dilute solution is evaporated in conditions set to form a concentrated solution containing, per kg, more than 186 g of sodium hydroxide, said concentrated solution is cooled to crystallize hydrated sodium hydroxide in mother water, hydrated sodium hydroxide is collected , it is heated to a temperature sufficient to melt it and the sodium amalgam is treated with molten hydrated sodium hydroxide. In this embodiment of the process according to the invention, the molten hydrated sodium hydroxide constitutes the above-mentioned aqueous medium, used to decompose the sodium amalgam.

Dans la forme de réalisation qui vient d'être exposée du procédé selon l'invention, la solution aqueuse diluée d'hydroxyde de sodium que l'on recueille de la réaction du carbonate de sodium avec la chaux contient par exemple, en général, entre 5 et 25% en poids d'hydroxyde de sodium, plus généralement entre 8 et 15%. Elle est généralement contaminée par des matières en solution, provenant des réactifs utilisés dans la réaction de caustification (carbonate de sodium et chaux), notamment du carbonate de sodium, du chlorure de sodium et du sulfate de sodium. Conformément à l'invention, on la concentre en la soumettant à une évaporation réglée pour amener sa teneur en hydroxyde de sodium dissous au-dessus de 186,0 g/kg et de préférence au-dessous de 743 g/kg, qui sont les teneurs corres­pondant respectivement au mélange eutectique de la glace et de l'hydroxyde de sodium heptahydraté, d'une part, et au mélange eutectique des composés NaOH et NaOH.1H₂O, d'autre part. La solution concentrée recueillie de l'évaporation est ensuite refroidie pour cristalliser de l'hydroxyde de sodium hydraté dans une eau mère. La température du refroidissement dépend de la concentration de la solution concentrée d'hydroxyde de sodium recueillie de l'évaporation, et elle peut aisément être déterminée au moyen du diagramme des phases du système NaOH - H₂O (P. PASCAL, "Nouveau traité de chimie minérale", Tome II, Premier fascicule, Masson et Cie, éditeurs, 1966, pages 254 à 258). Dans cette forme de réalisation du procédé selon l'invention, on peut mettre en oeuvre la technique décrite dans le document US-A-1733879. Pour recueillir l'hydroxyde de sodium hydraté, on peut faire usage de tout moyen capable de le séparer de l'eau mère, par exemple une filtration, une décantation ou une centri­fugation.In the embodiment which has just been described of the process according to the invention, the dilute aqueous solution of sodium hydroxide which is collected from the reaction of sodium carbonate with lime contains for example, in general, between 5 and 25% by weight of sodium hydroxide, more generally between 8 and 15%. It is generally contaminated with solids, coming from the reagents used in the causticization reaction (sodium carbonate and lime), in particular sodium carbonate, sodium chloride and sodium sulphate. In accordance with the invention, it is concentrated by subjecting it to controlled evaporation to bring its dissolved sodium hydroxide content above 186.0 g / kg and preferably below 743 g / kg, which are the contents corresponding respectively to the eutectic mixture of ice and sodium hydroxide heptahydrate, on the one hand, and to the eutectic mixture of the compounds NaOH and NaOH.1H₂O, on the other hand. The concentrated solution collected from evaporation is then cooled to crystallize hydrated sodium hydroxide in mother liquor. The cooling temperature depends on the concentration of the concentrated sodium hydroxide solution collected from evaporation, and it can easily be determined by means of the phase diagram of the NaOH - H₂O system (P. PASCAL, "New treatise on chemistry mineral ", Tome II, Premier fascicule, Masson et Cie, éditeurs, 1966, pages 254 to 258). In this embodiment of the method according to the invention, the technique described in document US-A-1733879 can be used. To collect the hydrated sodium hydroxide, any means capable of separating it from the mother liquor can be used, for example filtration, decantation or centrifugation.

Cette forme de réalisation du procédé selon l'invention présente l'avantage d'éviter la présence d'impuretés dans le milieu aqueux susmentionné, utilisé pour décomposer l'amalgame de sodium.This embodiment of the process according to the invention has the advantage of avoiding the presence of impurities in the above-mentioned aqueous medium, used to decompose the sodium amalgam.

Dans une variante avantageuse de la forme de réalisation décrite plus haut du procédé selon l'invention, l'évaporation de la solution diluée est réglée de manière que la solution aqueuse concentrée contienne, par kg, entre environ 468 et 321 g d'hydro­xyde de sodium, qui sont les teneurs correspondant respectivement au mélange eutectique des composés NaOH.3,5H₂O et NaOH.2H₂O, d'une part, et à la solution aqueuse saturée en hydroxyde de sodium à la température de cet eutectique, d'autre part. Dans l'exécution de cette variante de réalisation du procédé selon l'invention, il est souhaitable que la solution aqueuse concen­trée recueillie de l'évaporation présente une concentration en hydroxyde de sodium notablement différente de 388,3 g/kg, (correspondant au composé défini NaOH.3,5H₂O), de manière à faciliter le passage des impuretés dans l'eau mère au cours de la cristallisation par refroidissement. Pour des considérations de nature économique, il est préférable que la solution concentrée recueillie de l'évaporation ait une concentration en hydroxyde de sodium inférieure à 388,3 g/kg.In an advantageous variant of the embodiment described above of the process according to the invention, the evaporation of the dilute solution is controlled so that the concentrated aqueous solution contains, per kg, between approximately 468 and 321 g of hydroxide. sodium, which are the contents corresponding respectively to the eutectic mixture of the compounds NaOH.3,5H₂O and NaOH.2H₂O, on the one hand, and to the saturated aqueous solution of hydroxide of sodium at the temperature of this eutectic, on the other hand. In carrying out this variant embodiment of the method according to the invention, it is desirable that the concentrated aqueous solution collected from evaporation has a concentration of sodium hydroxide markedly different from 388.3 g / kg, (corresponding to the compound defined NaOH.3,5H₂O), so as to facilitate the passage of impurities in the mother liquor during crystallization by cooling. For economic considerations, it is preferable that the concentrated solution collected from evaporation has a sodium hydroxide concentration of less than 388.3 g / kg.

Dans la variante qui vient d'être décrite du procédé selon l'invention, le refroidissement de la solution concentrée est opéré à une température comprise entre, d'une part, la tempé­rature de solidification du mélange eutectique des composés NaOH.3,5H₂O et NaOH.2H₂O (environ 5°C) et, d'autre part, la température de fusion du composé défini NaOH.3,5H₂O (environ 16°C).In the variant which has just been described of the process according to the invention, the cooling of the concentrated solution is carried out at a temperature between, on the one hand, the solidification temperature of the eutectic mixture of the compounds NaOH.3,5H₂O and NaOH.2H₂O (approximately 5 ° C) and, on the other hand, the melting temperature of the defined compound NaOH.3.5H₂O (approximately 16 ° C).

Le procédé selon l'invention permet une flexibilité dans le fonctionnement des cellules d'électrolyse à mercure, en permettant d'adapter la fonctionnement des cellules au marché de l'hydroxyde de sodium, sans influencer la production du chlore.The method according to the invention allows flexibility in the operation of mercury electrolysis cells, by making it possible to adapt the operation of the cells to the sodium hydroxide market, without influencing the production of chlorine.

Des particularités et détails de l'invention vont ressortir de la description suivante de la figure unique du dessin annexé, qui représente le schéma d'une installation mettant en oeuvre une forme de réalisation particulière du procédé selon l'invention.Special features and details of the invention will emerge from the following description of the single figure of the appended drawing, which represents the diagram of an installation implementing a particular embodiment of the method according to the invention.

L'installation représentée à la figure comprend une unité de caustification de carbonate de sodium et une unité d'électrolyse.The installation shown in the figure includes a causticization unit of sodium carbonate and an electrolysis unit.

Dans l'unité de caustification, on introduit une solution aqueuse de carbonate de sodium 2 et de la chaux vive 3 dans une chambre de réaction 1. On recueille de la chambre de réaction 1 une suspension aqueuse 4 comprenant principalement du carbonate de calcium en suspension dans une solution aqueuse d'hydroxyde de sodium. La suspension 4 est traitée dans une chambre de décan­tation 5, de laquelle on recueille séparément un précipité de carbonate de calcium 6 et une solution aqueuse diluée d'hydroxyde de sodium 7. Le précipité 6 contient généralement une quantité non négligeable d'hydroxyde de calcium. On l'envoie dans une seconde chambre de réaction 8 qui est par ailleurs alimentée avec une solution aqueuse de carbonate de sodium 9. Après traitement sur un filtre 10 pour en séparer les matières insolubles 11, la solution aqueuse 12 est recyclée dans la chambre de réaction 1. La solution 7 recueillie de la chambre de décantation 5 contient par exemple entre 8 et 15% en poids d'hydroxyde de sodium. Elle est par ailleurs contaminée par diverses impuretés dissoutes, notamment du sulfate de sodium, du carbonate de sodium et du chlorure de sodium. Elle est envoyée dans un évaporateur 13 où on la concentre jusqu'à une teneur en hydroxyde de sodium comprise entre 321 et 388,3 g/kg. L'évaporation a pour résultat d'éliminer de l'eau 14 et de précipiter une partie des impuretés, principa­lement du sulfate de sodium et du carbonate de sodium que l'on évacue en 15. La solution aqueuse concentrée 16 que l'on recueille de l'évaporateur 13 est ensuite traitée dans un réfri­gérant 17, où on la refroidit à une température comprise entre 5 et 16°C, de manière à cristalliser le composé NaOH.3,5H₂O dans une eau mère. On recueille séparément le composé cristallisé 18 et l'eau mère 30. Le composé cristallisé 18 est essentiellement constitué d'hydroxyde de sodium hydraté de formule NaOH.3,5H₂O. On l'envoie dans une chambre de stockage 19, où on le réchauffe à une température supérieure à sa température de fusion (15,9°C), par exemple à la température ambiante, de manière à obtenir une solution aqueuse 20 contenant environ 388,3 g d'hydroxyde de sodium par kg. L'eau mère 30 est une solution aqueuse d'hydroxyde de sodium. Elle est recyclée dans l'évaporateur 13, après en avoir soutiré une purge 31.In the caustification unit, an aqueous solution of sodium carbonate 2 and quicklime 3 are introduced into a reaction chamber 1. An aqueous suspension 4 is collected from the reaction chamber 1 comprising mainly calcium carbonate in suspension in an aqueous solution of sodium hydroxide. The suspension 4 is treated in a settling chamber 5, from which a precipitate of calcium carbonate 6 and a dilute aqueous hydroxide solution are collected separately. sodium 7. The precipitate 6 generally contains a non-negligible amount of calcium hydroxide. It is sent to a second reaction chamber 8 which is also supplied with an aqueous solution of sodium carbonate 9. After treatment on a filter 10 to separate the insoluble materials 11, the aqueous solution 12 is recycled to the reaction 1. The solution 7 collected from the settling chamber 5 contains for example between 8 and 15% by weight of sodium hydroxide. It is also contaminated with various dissolved impurities, in particular sodium sulfate, sodium carbonate and sodium chloride. It is sent to an evaporator 13 where it is concentrated to a sodium hydroxide content of between 321 and 388.3 g / kg. Evaporation has the result of removing water 14 and precipitating part of the impurities, mainly sodium sulfate and sodium carbonate which are removed at 15. The concentrated aqueous solution 16 which is collected evaporator 13 is then treated in a refrigerant 17, where it is cooled to a temperature between 5 and 16 ° C, so as to crystallize the compound NaOH.3,5H₂O in mother liquor. The crystallized compound 18 and the mother liquor 30 are collected separately. The crystallized compound 18 essentially consists of hydrated sodium hydroxide of formula NaOH.3.5H₂O. It is sent to a storage chamber 19, where it is heated to a temperature above its melting temperature (15.9 ° C), for example at room temperature, so as to obtain an aqueous solution 20 containing approximately 388 , 3 g of sodium hydroxide per kg. The mother liquor 30 is an aqueous solution of sodium hydroxide. It is recycled in the evaporator 13, after having drawn off a purge 31.

L'unité d'électrolyse comprend une cellule d'électrolyse 21 du type à cathode de mercure, associée à un décomposeur d'amal­game de sodium 22. Des unités d'électrolyse de ce type sont bien connues en technique (J. S. SCONCE, "Chlorine, its manufacture, properties and uses" Reinhold Publishing Corporation, 1962, pages 127 à 199). La cellule d'électrolyse 21 comprend, de manière connue, une cathode horizontale de mercure (non représentée à la figure), en écoulement sur la sole de la cellule et des anodes (non représentées) disposées en regard du film de mercure, à courte distance de celui-ci. On fait circuler une solution aqueuse de chlorure de sodium 23 dans la cellule, au contact du film de mercure et des anodes. La solution aqueuse est décomposée par l'électrolyse et on recueille du chlore 24, un amalgame de sodium 25 et une solution aqueuse appauvrie en chlorure de sodium 29. L'amalgame de sodium contient par exemple entre 2,5 et 4 g de sodium par kg. Il est envoyé dans le décom­poseur 22 où on le fait circuler à contre-courant de la solution aqueuse d'hydroxyde de sodium 20 fabriquée dans l'unité de caustification. Dans le décomposeur 22 l'amalgame de sodium 25 et la solution aqueuse 20 sont mis en contact avec des éléments en graphite (non représentés au dessin). L'amalgame de sodium est décomposé progressivement par réaction avec l'eau, conduisant à la génération d'hydrogène 26. On recueille du mercure (ou un amalgame appauvri en sodium) 27 que l'on recycle dans la cellule d'électrolyse 21 et une lessive aqueuse d'hydroxyde de sodium 28.The electrolysis unit comprises an electrolysis cell 21 of the mercury cathode type, associated with a sodium amalgam decomposer 22. Electrolysis units of this type are well known in the art (JS SCONCE, "Chlorine , its manufacture, properties and uses "Reinhold Publishing Corporation, 1962, pages 127 to 199). The electrolysis cell 21 comprises, in known manner, a horizontal mercury cathode (not shown in the figure), flowing over the bottom of the cell and anodes (not shown) arranged opposite the mercury film, at a short distance from it. An aqueous solution of sodium chloride 23 is circulated in the cell, in contact with the film of mercury and the anodes. The aqueous solution is decomposed by electrolysis and chlorine 24, a sodium amalgam 25 and an aqueous solution depleted in sodium chloride 29 are collected. The sodium amalgam contains for example between 2.5 and 4 g of sodium per kg. It is sent to the decomposer 22 where it is circulated against the current of the aqueous sodium hydroxide solution 20 produced in the causticization unit. In the decomposer 22 the sodium amalgam 25 and the aqueous solution 20 are brought into contact with graphite elements (not shown in the drawing). The sodium amalgam is gradually decomposed by reaction with water, leading to the generation of hydrogen 26. Mercury (or a sodium-depleted amalgam) 27 is collected 27 which is recycled in the electrolysis cell 21 and an aqueous detergent of sodium hydroxide 28.

Claims (7)

1 - Procédé de fabrication d'une lessive d'hydroxyde de sodium, selon lequel on décompose un amalgame de sodium avec un milieu aqueux contenant de l'hydroxyde de sodium dissous, caractérisé en ce qu'on met en oeuvre de l'hydroxyde de sodium provenant du traitement d'une solution aqueuse de carbonate de sodium avec de la chaux.1 - Process for the manufacture of a sodium hydroxide solution, according to which a sodium amalgam is broken down with an aqueous medium containing dissolved sodium hydroxide, characterized in that sodium hydroxide is used sodium from the treatment of an aqueous solution of sodium carbonate with lime. 2 - Procédé selon la revendication 1, caractérisé en ce qu'à l'issue du traitement de la solution de carbonate de sodium avec la chaux, on recueille une solution diluée d'hydroxyde de sodium, on soumet ladite solution diluée à une évaporation dans des conditions réglées pour former une solution concentrée contenant, par kg, entre 188,0 et 468 g d'hydroxyde de sodium, on refroidit ladite solution concentrée pour cristalliser de l'hydroxyde de sodium hydraté que l'on recueille et que l'on chauffe à une température suffisante pour le fondre, et on traite l'amalgame de sodium avec l'hydroxyde de sodium hydraté fondu.2 - Process according to claim 1, characterized in that at the end of the treatment of the sodium carbonate solution with lime, a dilute solution of sodium hydroxide is collected, said dilute solution is subjected to evaporation in conditions set to form a concentrated solution containing, per kg, between 188.0 and 468 g of sodium hydroxide, said concentrated solution is cooled to crystallize hydrated sodium hydroxide which is collected and which is heats to a temperature sufficient to melt, and the sodium amalgam is treated with molten hydrated sodium hydroxide. 3 - Procédé selon la revendication 2, caractérisé en ce qu'on règle l'évaporation pour que la solution concentrée contienne, par kg, entre 321 et 468 g d'hydroxyde de sodium, et on refroidit la solution concentrée à une température comprise entre 5 et 16°C.3 - Process according to claim 2, characterized in that the evaporation is regulated so that the concentrated solution contains, per kg, between 321 and 468 g of sodium hydroxide, and the concentrated solution is cooled to a temperature between 5 and 16 ° C. 4 - Procédé selon la revendication 3, caractérisé en ce qu'on règle l'évaporation pour que la solution concentrée présente une teneur pondérale en hydroxyde de sodium inférieure à 388,3 g/kg.4 - Process according to claim 3, characterized in that the evaporation is regulated so that the concentrated solution has a weight content of sodium hydroxide less than 388.3 g / kg. 5. Procédé selon l'une quelconque des revendications 1 à 4, caractérisé en ce qu'on met en oeuvre une solution aqueuse de carbonate de sodium obtenue par débicarbonatation d'une solution saturée de bicarbonate de sodium.5. Method according to any one of claims 1 to 4, characterized in that an aqueous solution of sodium carbonate obtained by debicarbonation of a saturated solution of sodium bicarbonate is used. 6 - Procédé selon l'une quelconque des revendications 1 à 5, caractérisé en ce qu'on met en oeuvre un amalgame de sodium contenant entre 1 et 5 g de sodium par kg.6 - Method according to any one of claims 1 to 5, characterized in that one implements a sodium amalgam containing between 1 and 5 g of sodium per kg. 7 - Procédé selon la revendication 6, caractérisé en ce qu'on met en oeuvre un amalgame de sodium obtenu par électrolyse d'une solution aqueuse de chlorure de sodium dans une cellule d'électrolyse à cathode de mercure.7 - Method according to claim 6, characterized in that one implements a sodium amalgam obtained by electrolysis of an aqueous solution of sodium chloride in an electrolysis cell with mercury cathode.
EP90202143A 1989-08-17 1990-08-06 Process for manufacturing a sodium hydroxide caustic solution Withdrawn EP0413385A1 (en)

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FR2729133A1 (en) * 1995-01-11 1996-07-12 Solvay PROCESS FOR COPRODUCTION OF CALCIUM CARBONATE AND SODIUM HYDROXIDE

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EP2871156A1 (en) * 2013-11-12 2015-05-13 Solvay SA Process for treating a sodium carbonate purge
CN107973322A (en) * 2017-12-15 2018-05-01 沈阳市好太阳日用品加工厂 Environment-friendly novel sodium hydroxide powder agent
CN114921663B (en) * 2022-06-14 2023-11-21 厦门钨业股份有限公司 Method for extracting tungsten from scheelite

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CH264595A (en) * 1945-12-20 1949-10-31 Solvay Process for the causticization of sodium carbonate.
US3321388A (en) * 1962-08-09 1967-05-23 Asahi Denka Kogyo Kk Process for coordinated operation of diaphragm and mercury cathode electrolytic cells
EP0035128A1 (en) * 1980-03-03 1981-09-09 Uhde GmbH Process for concentrating a low-percentage caustic soda solution

Patent Citations (3)

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CH264595A (en) * 1945-12-20 1949-10-31 Solvay Process for the causticization of sodium carbonate.
US3321388A (en) * 1962-08-09 1967-05-23 Asahi Denka Kogyo Kk Process for coordinated operation of diaphragm and mercury cathode electrolytic cells
EP0035128A1 (en) * 1980-03-03 1981-09-09 Uhde GmbH Process for concentrating a low-percentage caustic soda solution

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2729133A1 (en) * 1995-01-11 1996-07-12 Solvay PROCESS FOR COPRODUCTION OF CALCIUM CARBONATE AND SODIUM HYDROXIDE
WO1996021620A1 (en) * 1995-01-11 1996-07-18 Solvay (Societe Anonyme) Method for coproducing calcium carbonate and sodium hydroxide
US5993772A (en) * 1995-01-11 1999-11-30 Solvay (Societe Anonyme) Method for coproducing calcium carbonate and sodium hydroxide

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